A normal labor process is divided into three stages. Among these stages, the first and second stages are the crucial ones which are directly involved in the delivery of fetus. The first stage of labor begins with the onset of rhythmic uterine contraction and ends at the complete dilation of the cervix which is about 10 cm in diameter. The complete dilation of the cervix marks the beginning of the second stage of labor which ends immediately after the birth of the fetus. The third stage of labor extends from the birth of the baby to the complete expulsion of the placenta. The labor progress is driven by two types of labor forces. The primary force is produced by the involuntary contractions of uterine muscle. The secondary force is produced by the increase of intra-abdominal pressure through voluntary contractions of the abdominal muscles and diaphragm. These forces cause an increase of intrauterine pressure to provide a critical expulsion force on fetus.
As often seen in clinical practice, systemic analgesic drugs, epidural anesthesia and long duration of exhaustive labor all can lead to the weakening of secondary force, and sequentially to delayed labor duration or even dystocia (arrest of labor). Numerous clinical studies have correlated a prolonged labor duration and dystocia with many undesirable outcomes, such as higher rate of infant mortality, neonatal seizures and postpartum hemorrhage. To solve these serious problems, clinical instruments (forceps or vacuum suction) or cesarean section are often required to terminate labors. However, both instrumental delivery and cesarean section are far from trouble-free. While a cesarean section is basically safe, it remains a major surgical procedure. Patients who give birth by cesarean section are at much greater risk of childbirth-related illness or death than women who deliver vaginally. Also, the average cesarean birth has a length of hospital stay double that of a normal delivery and costs up to three times as much. Instrumental delivery also has limitations and may result in numerous complications including head and facial injuries to fetus. Therefore, it is in the best interest of both mother and fetus to prevent the incidence of prolonged duration of labor or dystocia.
One method of decreasing the incidence of prolonged labor is oxytocin infusion, which is commonly used in clinical practice to increase the primary labor force by directly inducing uterine contraction. Clinical evidence has demonstrated that oxytocin alone can only partially solve the problem of prolonged labor and dystocia associated with epidural anesthesia. However, a high incidence of cesarean section still occurs in patients receiving epidural anesthesia in spite of a high dosage of oxytocin infusion. Furthermore, high doses of oxytocin has been implicated in uterine tetanus and in some adverse neonatal outcomes, including fetal asphyxia.
Devices directed toward assisting in delivery are disclosed in the prior art. In the apparatus of Heidenwolf (U.S. Pat. No. 2,597,637, issued May 20, 1952), an inflatable bladder is held against the woman's upper abdomen by a wide belt. Extending from the bottom of the belt is a pair of straps which, in turn, attaches to straps surrounding the upper thighs. This structure holds the belt down to prevent slippage.
In the birth-assisting pneumatic cuff of Lee (U.S. Pat. No. 5,174,281, issued Dec. 29, 1992), an inflatable bladder fits over and around the woman's abdomen and is manually inflated and deflated in coordination with the patient's voluntary straining during the second stage of labor. This device applies pressure equally to the entire abdomen.
The Chinese patent of Fei Chao (Chinese Patent No. 2198, issued in 1989) teaches an abdominal girdle which has a generally triangular bladder (to match the rough contour of the uterus) which is placed over the patient's abdomen. The bladder is inflated manually in coordination with the woman's contractions to apply a downward pressure on the abdomen, assisting in forcing the fetus downward. While the girdle itself is very effective, the manual control of the inflation/deflation may not be easily accepted by physicians who may be reluctant to rely on a device which could be easily subject to human error with serious consequences.
Related prior art may be seen in the areas of anti-G pressure suits and in inflatable tourniquets and splits. Examples of pressure suits are taught by Crosbie et al. in U.S. Pat. No. 4,534,338, issued Aug. 13, 1985, and Van Patten, U.S. Pat. No. 4,736,731, issued Apr. 12, 1988. These suits inflate in response to changes in the rate of acceleration of an aircraft. Poole, et al. (U.S. Pat. No. 4,531,516, issued Jul. 30, 1985), Manes (U.S. Pat. No. 4,548,198, issued Oct. 22, 1985) and Kitchin et al. (U.S. Pat. No. 4,520,820, issued Jun. 4, 1985) teach inflatable devices for first aid applications. The latter two patents include disclosure of controllers for maintaining constant pressure, however none of these patents addresses synchronization of inflation/deflation as would be required for a labor- and delivery-assisting device.